Collected platelets intended for transfusion are highly perishable. Platelets are non-nucleated bone marrow-derived blood cells that protect injured mammals from blood loss by adhering to sites of vascular injury and by promoting the formation of plasma fibrin clots. Humans depleted of circulating platelets by bone marrow failure suffer from life threatening spontaneous bleeding, and less severe deficiencies of platelets contribute to bleeding complications following trauma or surgery.
As the count of circulating platelets falls (e.g., ˜70,000 per μL), patients become increasingly susceptible to cutaneous bleeding. Patients with platelet counts of less than 20,000 per μL are highly susceptible to spontaneous hemorrhage from mucosal surfaces, especially when the thrombocytopenia is caused by a bone marrow disorder or failure. Platelet deficiencies associated with bone marrow disorders such as aplastic anemia, acute and chronic leukemia, metastatic cancer, and deficiencies resulting from cancer treatment such as ionizing radiation or chemotherapy all contribute to a major public health problem. Patients that suffer from thrombocytopenia associated with major surgery, injury and sepsis also require significant numbers of platelet transfusions.
A major advance in medical care half a century ago was the development of platelet transfusions to correct such platelet deficiencies, resulting in about 2.6 million platelet transfusions in the United States per year at current transfusion rates. However, platelets collected for transfusion are highly perishable because, upon storage at or below room temperature, they quickly lose in vivo hemostatic activity. Hemostatic activity broadly refers to the ability of a population of platelets to mediate bleeding cessation.
Platelets, unlike all other transplantable tissues, do not tolerate refrigeration and disappear rapidly from the circulation of recipients if subjected to even very short periods of chilling. Importantly, the cooling effect that shortens in vivo platelet survival is thought to be irreversible and, therefore, cooled platelets become unsuitable for transfusion. One of the first visible effects of platelet impairment is an irreversible conversion from a discoid morphology towards a spherical shape, and the appearance of spiny projections on the surface of platelets due to calcium dependent gelsolin activation and phosphoinositide-mediated actin polymerization. When platelets are exposed to temperatures lower than 20° C., they rapidly undergo such shape modifications.
The need to keep platelets at room temperature prior to transfusion has imposed a unique set of costly and complex logistical requirements on platelet storage. Because platelets are metabolically active at room temperature, they require constant agitation in gas permeable containers to allow for the exchange of gases to prevent the toxic consequences of metabolic acidosis. Room temperature storage conditions result in macromolecular degradation and reduced hemostatic functioning of platelets, a set of defects known as the “platelet storage lesion” (PSL). In addition, storage at room temperature encourages the growth of bacteria, thereby creating a higher risk of bacterial infection, which effectively limits the duration of such storage to about 5 days. These bacteria include endogenous ones as well as skin-derived ones associated with venipuncture. In this regard, bacterial contamination of platelets is by far the most frequent infectious complication of blood component use. At current rates, from one in 1,000 to one in 2,000 units of platelets are contaminated with bacteria at a level sufficient to pose a significant risk to the recipient.
Thus, there remains a pressing need to develop agents, solutions and methods to (i) improve or prolong in vivo hemostatic activity of human platelets upon storage at or below room temperature, (ii) stabilize platelets during storage to prevent their premature clearance from circulation following transfusion, and (iii) more significantly, inhibit bacterial proliferation during room temperature platelet storage.